Digital control units have been used in many different ways in modern motor vehicles. They not only control the ignition and/or fuel-injection operations, but also perform a multitude of additional functions, such as controlling the gear unit, regulating exhaust gas, braking, skidding, and the like. Combined control operations can also be integrated into one control unit.
The main storage containing control data and operating programs is usually designed as a permanent storage. The main storage may be embodied as a ROM or EPROM. German Patent 4128900, for example, discloses this type of control unit with a permanent storage. The disadvantage of this permanent storage is that it is very difficult to make subsequent modifications of the data or programs. To make such modifications, the appropriate permanent storage must be unsoldered and replaced by another one. Generally, the entire printed circuit board or the entire control unit must be exchanged. Therefore, almost exclusively, only new vehicles are able to undergo software improvements or have software functions added, while vehicles which have already been delivered do not do so for cost reasons.
Another consequence of using these permanent storage units is that one type of motor vehicle invariably contains the same program and the same control data, so that adaptations to individual preference and driving style are not possible.
The use of a read/write memory as the main storage so that the operating programs or control data can be modified is known from the use of emulation devices for the test phase of a motor vehicle. However, this requires the use of a special control unit with interchangeable storage units and an external programming device to allow the programs and data to be modified. These types of control units, therefore, cannot be used for serial applications.